Battery Recomendation

Lynxmotion
1

So, as LM phases out all of their 7.2V electronics, none of my 7.2V NiMHs will work for my upcoming robot adventures. My current charger won’t do 12V NiMH, so anything higher and I am already looking at new equipment.

So, I am looking for some opinions:

  1. Is LiPo the way to go? Or are 12V NiMH still competitive?

  2. If I go with LiPo, should I get a 3S or a 4S pack? I want to be able to power either a hexapod or a tritrack with the same battery size (so, it has to be capable of driving LM’s 12V motors at least)

  3. As far as BECs go, how much current do the HS645MG hexapods draw?

  4. Chargers, which one do you have?

Also, if anyone has any experiences with brands, both good and negative, I would love to hear about it. Same for particular products. Investing in a new battery technology is going to run several hundred dollars I think, and I want to get all the information before taking a plunge.

Thanks!
Sienna

2

NiMH is very must alive and well. LiPo have special handling requirements that make them a little more difficult to work with. They offer great performance though. The 645 hexapods draw around 7-8 amps when walking.

3

LM is phasing out 7.2V electronics?

This is going to be tricky. The LiPo packs that R/C cars use are generally around 7.2V (possibly closer to 9.0V open circuited after a full charge). If you are directly driving this into the VS+ (servo’s power) of the SSC-32 for your servos, this could be a problem. You would most likely need to regulate it down to 6.0V with a really good heat-sunk regulator. A solution would be to use two 6.0V packs in series for your tritrack and use them individually for hexapods. Just remember to “equalize” your battery packs as much as you can when hooking them up in series. What I mean is discharge both 6.0V packs down to same level after use. For Sub-C NiMH, I generally like to discharge each cell to about 0.9V. So for a 5-cell, discharge the pack down to about 4.5V. Then hook them up in series and charge them as if it was one pack. I would opt for a good charger with a lot of oomph like the LRP Pulsar 2 or Duratrax ICE. The ICE has a nice feature that it can charge certain LiPos…

BECs are circuits that were designed primarily for R/C use, so that when the battery is nearly discharged, the power to the steering servos are still provided so that the vehicle doesn’t veer off into a wall :wink: Not sure what purpose it can serve a walking bot or a tritrack if it’s not going nearly at the speed of R/C cars…

I use LRP’s Pulsar 2 charger from my R/C days coupled with a 12V, 25A power supply bought at Radio Shack (roughly $100 around 4 years ago) (Pulsar needs a DC input, it does not have a AC to DC transformer inside). I’ve seen many people use the Duratrax ICE charger at the track also, they have similar features as the Pulsar 2 if not more. You do have to be careful with the settings in these chargers, they were primarily meant for Sub-C cells. I charge my 5-cell AA packs at 1.0A charge rate, and the charge voltage is 14.5V I believe. For my 2500mAH packs, it takes just a little under 2 hours to charge.

4

Well, we are discontinuing 7.2vdc motors. We are out of the 7.2vdc 2800mAh packs but we are getting more.

But we don’t sell any electronics that are 7.2vdc only.

5

Yeah, I meant the motors… :blush

I was actually looking at the LiPo packs that go into R/C airplanes. Those you can get 3S (around 11V) or 4S (around 14V). I guess my real question, is how much voltage can the LM planetary gear motors stand for extended periods of time?

Yeah, I looked at the ICE, and it only goes to 4S. To me, that is cutting it too close to be a real investment. Nor is it directly a balance charger, so I would still have to get an inline balancer.

I was looking at the Triton2, which goes to 5S. To me, that is more future proof then the ICE for LiPo. However, there is a new one come out from Great Planes that looks like it will be ideal (sometime around march I think)

I was looking at the Dimension Engineering BECs, which are switched regulators. Their Sport BEC takes in LiPo voltages, and turns it into 6V at 3.5A. I would be using those to power servos. Hence, why I was asking how many amps a hex draws, so I can size my BECs correctly (e.g., get a number of them in parallel).

6

Word of caution with LiPos:

Make sure you take care not to drop it or shock the packs. The R/C car LiPos comes in a hard case for a reason. They are very sensitive to shock and can be shorted internally if subjected to it and possibly leak/explode! :smiling_imp: